Selective removal of charge-trapping layer for select gate transistors and dummy memory cells in 3D stacked memory

ABSTRACT

Fabrication techniques for a three-dimensional stack memory device remove the charge-trapping material from the select gate transistors and the dummy memory cells to avoid unintentional programming which increases the threshold voltage. In one approach, a stack is formed with a different sacrificial material for the a) control gate layers of the select gate transistors and the dummy memory cells and the b) control gate layers of the data memory cells. A slit is formed to allow etchants to be introduced to selectively remove the sacrificial material and then the charge-trapping material for the select gate transistors and dummy memory cells. Subsequently, an etchant is introduced to remove the sacrificial material but not the charge-trapping material for the data memory cells. In other approaches, a protective layer is provided partway in the slit, or the slit is etched in two steps, and a common sacrificial material can be used.

BACKGROUND

The present technology relates to the fabrication of a memory device.

A charge-trapping material can be used in memory devices to store acharge which represents a data state. The charge-trapping material canbe arranged vertically in a three-dimensional (3D) stacked memorystructure, or horizontally in a two-dimensional (2D) memory structure.One example of a 3D memory structure is the Bit Cost Scalable (BiCS)architecture which comprises a stack of alternating conductive anddielectric layers. A memory hole is formed in the stack and a NANDstring is then formed by filling the memory hole with materialsincluding a charge-trapping layer. A straight NAND string extends in onememory hole, while a pipe- or U-shaped NAND string (P-BiCS) includes apair of vertical columns of memory cells which extend in two memoryholes and which are joined by a bottom back gate. Control gates of thememory cells and of select gate transistors are provided by theconductive layers.

However, various challenges are presented in operating such memorydevices.

BRIEF DESCRIPTION OF THE DRAWINGS

Like-numbered elements refer to common components in the differentfigures.

FIG. 1A is a perspective view of a set of blocks in a 3D stackednon-volatile memory device.

FIG. 1B is a functional block diagram of a memory device such as the 3Dstacked non-volatile memory device 100 of FIG. 1A.

FIG. 2A depicts a top view of example word line layers 202 and 204 in aU-shaped NAND embodiment, as an example implementation of BLK0 in FIG.1A.

FIG. 2B depicts a top view of example select gate layer portions,consistent with FIG. 2A.

FIG. 2C depicts an embodiment of a stack 231 showing a cross-sectionalview of the portion 209 of FIG. 2A, along line 220, where select gatelayers SGL1 and SGL2 are provided.

FIG. 2D depicts an alternative view of the select gate layers and wordline layers of the stack 231 of FIG. 2C.

FIG. 3A depicts a top view of an example word line layer 304 of theblock BLK0 of FIG. 1A, in a straight NAND string embodiment.

FIG. 3B depicts a top view of an example SGD layer 362, consistent withFIG. 3A.

FIG. 3C depicts an embodiment of a stack 376 showing a cross-sectionalview of the portion 307 of FIG. 3A, along line 305.

FIG. 3D depicts an alternative view of the select gate layers and wordline layers of the stack 376 of FIG. 3C.

FIG. 4A depicts a top view of an example word line layer 400 of theblock BLK0 of FIG. 1A, in another straight NAND string embodiment.

FIG. 4B depicts a top view of an example SGD layer 420, consistent withFIG. 4A.

FIG. 4C depicts an embodiment of a stack 440 showing a cross-sectionalview along line 412 of FIG. 4A and line 412 a of FIG. 4B.

FIG. 4D depicts an alternative view of the select gate layers and wordline layers of the stack 440 of FIG. 4C.

FIG. 4E depicts a view of the region 246 of FIG. 3C or the region 442 ofFIG. 4C1, where a blocking oxide layer is provided along the sidewall ofthe memory hole.

FIG. 4F depicts a view of the region 246 of FIG. 3C or the region 442 ofFIG. 4C1, where a blocking oxide layer is provided within the controlgate layers.

FIG. 4G depicts an overview of the fabrication process of FIG. 5.

FIG. 5 depicts a fabrication process for a 3D stack in a memory devicein which a charge-trapping material is removed from select gatetransistors and/or dummy memory cells.

FIG. 6A depicts a semiconductor structure 600 comprising a stack ofalternating control gate layers and dielectric layers in accordance withsteps 500 and 500 a of FIG. 5.

FIG. 6B depicts a semiconductor structure 605 comprising a stack ofalternating control gate layers and dielectric layers in accordance withsteps 500 and 500 a of FIG. 5, in an option where source-side controlgate layers also have a different sacrificial material than the controlgate layers of the data memory cells.

FIG. 6C depicts a semiconductor structure 610 obtained by processing thesemiconductor structure of FIG. 6A in accordance with step 501 of FIG.5.

FIG. 6D depicts a semiconductor structure 620 obtained by processing thesemiconductor structure of FIG. 6C in accordance with step 503 of FIG.5.

FIG. 6E depicts a semiconductor structure 630 obtained by processing thesemiconductor structure of FIG. 6D in accordance with step 504 of FIG.5.

FIG. 6F depicts a semiconductor structure 640 obtained by processing thesemiconductor structure of FIG. 6E in accordance with step 505 of FIG.5.

FIG. 6G depicts a semiconductor structure 650 obtained by processing thesemiconductor structure of FIG. 6F in accordance with step 507 of FIG.5, in an option in which the sacrificial material is removed for thedrain-side select gate layers and dummy memory cells.

FIG. 6H1 depicts a semiconductor structure 659 which is an alternativeto the semiconductor structure of FIG. 6G, in an option in which thesacrificial material is also removed for the source-side select gatelayers and dummy memory cells, consistent with the semiconductorstructure of FIG. 6B.

FIG. 6H2 depicts a semiconductor structure 659 a obtained by processingthe semiconductor structure of FIG. 6H1 in accordance with step 508 ofFIG. 5.

FIG. 6I depicts a semiconductor structure 660 obtained by processing thesemiconductor structure of FIG. 6G in accordance with step 508 and 509of FIG. 5, where the tunneling material remains.

FIG. 6J depicts a semiconductor structure 665 obtained by processing thesemiconductor structure of FIG. 6I in accordance with step 509 a of FIG.5, where the tunneling material is etched away and a dopant isintroduced laterally to the channel material.

FIG. 6K depicts a semiconductor structure 670 obtained by processing thesemiconductor structure of FIG. 6I in accordance with step 511 of FIG.5.

FIG. 6L depicts a semiconductor structure 680 obtained by processing thesemiconductor structure of FIG. 6K in accordance with step 513 of FIG.5, where metal is deposited in the voids and slits.

FIG. 6M depicts a semiconductor structure 682 obtained by processing thesemiconductor structure of FIG. 6L in accordance with step 513 of FIG.5, to remove the previously-deposited metal, provide an insulating layerin the slit, etch through the insulating layer at a bottom of the slit,and deposit additional metal to form metal-filled slits.

FIG. 6N depicts a semiconductor structure 685 obtained by processing thesemiconductor structure of FIG. 6M in accordance with step 514 of FIG.5.

FIG. 6O depicts a semiconductor structure 690 obtained by processing thesemiconductor structure of FIG. 6K in accordance with steps 512 and 513of FIG. 5.

FIG. 7A depicts a semiconductor structure 700 obtained by processing thesemiconductor structure of FIG. 6C in accordance with step 503 of FIG.5.

FIG. 7B depicts a semiconductor structure 710 obtained by processing thesemiconductor structure of FIG. 7A in accordance with steps 504, 505 and507 of FIG. 5.

FIG. 7C depicts a semiconductor structure 720 obtained by processing thesemiconductor structure of FIG. 7B in accordance with steps 509, 511,512 and 513 of FIG. 5.

FIG. 8A depicts a semiconductor structure 800 obtained by processing asemiconductor structure in accordance with step 500 b of FIG. 5.

FIG. 8B depicts a semiconductor structure 810 obtained by processing thesemiconductor structure of FIG. 8A in accordance with step 506 a of FIG.5.

FIG. 8C depicts a semiconductor structure 820 obtained by processing thesemiconductor structure of FIG. 8B in accordance with step 506 b of FIG.5.

FIG. 8D depicts a semiconductor structure 830 obtained by processing thesemiconductor structure of FIG. 8C in accordance with steps 507, 508 and509 of FIG. 5.

FIG. 9A depicts a semiconductor structure 900 obtained by processing thesemiconductor structure of FIG. 8A in accordance with step 505 of FIG.5.

FIG. 9B depicts a semiconductor structure 910 obtained by processing thesemiconductor structure of FIG. 9A in accordance with steps 507 and 509b of FIG. 5.

DETAILED DESCRIPTION

Techniques are provided for fabricating a 3D stacked non-volatile memorydevice in which the charge-trapping layer is removed from select gatetransistors and/or dummy memory cells. A corresponding 3D stackednon-volatile memory device is also provided.

A 3D stacked non-volatile memory device has a multi-layer configurationin which conductive layers alternate with dielectric layers in a stack.Memory holes are etched in the stack and films are deposited in theholes such that memory cells or select gate transistors are formed wherethe conductive layers intersect with the memory holes. The films caninclude a charge-trapping material, a tunneling material and a channelmaterial. Some of the conductive layers (e.g., control gate layers) areused as control gates for memory cells and other conductive layers areused as control gates for select gate transistors, such as drain- orsource-side transistors in NAND strings. The NAND strings extendvertically in the memory device. The charge-trapping material can besilicon nitride or other nitride, for instance. The memory cells caninclude data memory cells, which are eligible to store data, and dummymemory cells, which are not eligible to store data, but provide atransition region between a select gate and the data memory cells.

However, unintentional programming can occur for the select gatetransistors and/or dummy memory cells during program-erase (P-E)operations for the data memory cells. For example, during an eraseoperation, the channel of a NAND string is charged by biasing the selectgate transistors at the drain-side of the NAND string to generate holesby gate-induced drain leakage (GIDL). A relatively high erase voltage isapplied to the drain-side via a bit line while control gate voltages areset on the dummy memory cells and the select gate transistors. The holesdiffuse throughout the channel of the NAND string to charge up thechannel. However, it takes some time for the holes to diffuse. As aresult, at a beginning of the erase voltage, the dummy memory cells andthe select gate transistors will experience a relatively highgate-to-channel voltage which can induce weak Fowler-Nordheim (F-N)tunneling. This F-N tunneling gradually programs the dummy memory cellsand the select gate transistors over time as P-E cycles accumulate. Theresulting increase in the threshold voltage (Vth) of the dummy memorycells and the select gate transistors can impair the ability of the NANDstring to operate. For example, during sensing and programmingoperations, the increase in the Vth may prevent the dummy memory cellsand the select gate transistors from being fully conductive.

Fabrication processes provided herein remove portions of thecharge-trapping layer which are located in the control gate layers ofthe dummy memory cells and/or the select gate transistors so that thedummy memory cells and/or the select gate transistors cannot have theirVth increased due to unintentional programming. The dummy memory cellsand/or the select gate transistors no longer have a charge-trappingmaterial. The charge-trapping layer can be removed in a self-alignedmanner so that no additional lithography is required in the fabricationof the memory device. Moreover, these processes are compatible withexisting fabrication techniques.

In one approach, a first sacrificial material of the control gate layersfor the dummy memory cells and the select gate transistors is differentthan a second sacrificial material of the data memory cells. As aresult, when a slit is formed in the stack, an etchant can be introducedwhich is more selective of the first sacrificial material than of thesecond sacrificial material. For example, the first sacrificial materialcan comprise polysilicon while the second sacrificial material cancomprise silicon nitride. Horizontally-extending voids can thereby becreated in the control gate layers for the dummy memory cells and theselect gate transistors to expose portions of the charge-trappingmaterial in a memory hole. Another etchant can be introduced to removethe exposed portions of the charge-trapping material. Subsequently, afurther etchant can be introduced to remove the sacrificial material ofthe data memory cells to create voids in the control gate layers of thedata memory cells. Portions of the charge-trapping material in thecontrol gate layers for the data memory cells remain in the memorydevice.

A blocking oxide can be provided in the memory holes and/or the voids.Finally, a metal can be introduced which fill the voids to concurrentlyform control gate layers for the dummy memory cells, the select gatetransistors and the data memory cells.

The threshold voltages of the dummy memory cells and/or the select gatetransistors can be adjusted using a dopant. For example, in oneapproach, the dopant can be applied to the top of the stack using ionimplantation. In another possible approach, the dopant can be appliedlaterally in the voids. Both approaches could be combined as well.

In another possible approach, a common sacrificial material can be usedfor the control gate layers for the dummy memory cells, the select gatetransistors and the data memory cells. A slit is formed in the stack,and a protective layer is deposited and etched down in the slit to aspecified height which is between a bottommost control gate layer of thecontrol gate layers for the dummy memory cells and/or the select gatetransistors and a topmost control gate layer of the control gate layersfor the data memory cells. The sacrificial material of the control gatelayers for the dummy memory cells and/or the select gate transistors canthen be etched away to access the associated portions of thecharge-trapping material. Subsequently, the remainder of the protectivelayer is etched away and the sacrificial material of the control gatelayers for the data memory cells can be etched away. The blocking oxideand the metal can be provided as discussed.

In another possible approach, a common sacrificial material can be usedfor the control gate layers for the dummy memory cells, the select gatetransistors and the data memory cells. A slit is formed in the stack ina two etching steps. A first etch forms a slit which extends partwaythrough the stack, to the specified height mentioned above. Thesacrificial material of the control gate layers for the dummy memorycells and/or the select gate transistors can then be etched away toaccess the associated portions of the charge-trapping material.Subsequently, a second etch lowers the slit to the bottom of the stack.The sacrificial material of the control gate layers for the data memorycells can then be etched away. The blocking oxide and the metal canagain be provided as discussed.

Generally, there can be one or more drain-side select gate transistorsand one or more drain-side dummy memory cells in each NAND string.Further, the source-side of each NAND string can include one or moresource-side select gate transistors and one or more source-side dummymemory cells. The charge-trapping material can be removed from one ormore of these transistors or dummy memory cells in each NAND string. Thedummy memory cells and data memory cells are also transistors.

The following discussion provides details of the construction of examplememory devices and of related techniques which address the above andother issues.

FIG. 1A is a perspective view of a set of blocks in a 3D stackednon-volatile memory device. The memory device 100 includes a substrate101. On the substrate are example blocks BLK0, BLK1, BLK2 and BLK3 ofmemory cells (storage elements) and a peripheral area 104 with circuitryfor use by the blocks. For example, the circuitry can include voltagedrivers 105 which can be connected to control gate layers of the blocks.In one approach, control gate layers at a common height in the blocksare commonly driven. The substrate 101 can also carry circuitry underthe blocks, along with one or more lower metal layers which arepatterned in conductive paths to carry signals of the circuitry. Theblocks are formed in an intermediate region 102 of the memory device. Inan upper region 103 of the memory device, one or more upper metal layersare patterned in conductive paths to carry signals of the circuitry.Each block comprises a stacked area of memory cells, where alternatinglevels of the stack represent word lines. In one possible approach, thecontrol gate layers of each block at a common height are connected toone another and to a voltage driver. While four blocks are depicted asan example, two or more blocks can be used, extending in the x- and/ory-directions.

In one possible approach, the length of the plane, in the x-direction,represents a direction in which signal paths to word lines extend in theone or more upper metal layers (a word line or SGD line direction), andthe width of the plane, in the y-direction, represents a direction inwhich signal paths to bit lines extend in the one or more upper metallayers (a bit line direction). The z-direction represents a height ofthe memory device.

FIG. 1B is a functional block diagram of a memory device such as the 3Dstacked non-volatile memory device 100 of FIG. 1A. The memory device 100may include one or more memory die 108. The set of blocks of FIG. 1A canbe on one die. The memory die 108 includes a memory structure 126 ofmemory cells, such as an array of memory cells, control circuitry 110,and read/write circuits 128. In a 3D configuration, the memory structurecan include the blocks of FIG. 1A. The memory structure 126 isaddressable by word lines via a row decoder 124 and by bit lines via acolumn decoder 132. The read/write circuits 128 include multiple senseblocks SB1, SB2, . . . , SBp (sensing circuitry) and allow a page ofmemory cells to be read or programmed in parallel. Typically acontroller 122 is included in the same memory device 100 (e.g., aremovable storage card) as the one or more memory die 108. Commands anddata are transferred between the host 140 and controller 122 via a databus 120 and between the controller and the one or more memory die 108via lines 118.

The memory structure can be 2D or 3D. The memory structure may compriseone or more array of memory cells including a 3D array. The memorystructure may comprise a monolithic three dimensional memory structurein which multiple memory levels are formed above (and not in) a singlesubstrate, such as a wafer, with no intervening substrates. The memorystructure may comprise any type of non-volatile memory that ismonolithically formed in one or more physical levels of arrays of memorycells having an active area disposed above a silicon substrate. Thememory structure may be in a non-volatile memory device having circuitryassociated with the operation of the memory cells, whether theassociated circuitry is above or within the substrate.

The control circuitry 110 cooperates with the read/write circuits 128 toperform memory operations on the memory structure 126, and includes astate machine 112, an on-chip address decoder 114, and a power controlmodule 116. The state machine 112 provides chip-level control of memoryoperations. A storage region 113 may be provided for parameters foroperating the memory device.

The on-chip address decoder 114 provides an address interface betweenthat used by the host or a memory controller to the hardware addressused by the decoders 124 and 132. The power control module 116 controlsthe power and voltages supplied to the word lines and bit lines duringmemory operations. It can includes drivers for word line layers (WLLs)in a 3D configuration, SGS and SGD transistors and source lines. Thesense blocks can include bit line drivers, in one approach. An SGStransistor is a select gate transistor at a source end of a NAND string,and an SGD transistor is a select gate transistor at a drain end of aNAND string.

In some implementations, some of the components can be combined. Invarious designs, one or more of the components (alone or incombination), other than memory structure 126, can be thought of as atleast one control circuit which is configured to perform the actionsdescribed herein. For example, a control circuit may include any one of,or a combination of, control circuitry 110, state machine 112, decoders114/132, power control module 116, sense blocks SB1, SB2, . . . , SBp,read/write circuits 128, controller 122, and so forth.

The off-chip controller 122 may comprise a processor 122 c and storagedevices (memory) such as ROM 122 a and RAM 122 b. The storage devicescomprises code such as a set of instructions, and the processor isoperable to execute the set of instructions to provide the functionalitydescribed herein. Alternatively or additionally, the processor canaccess code from a storage device 126 a of the memory structure, such asa reserved area of memory cells in one or more word lines.

For example, code may be executed by the processor 122 c. The code isused by the controller to access the memory structure such as forprogramming, read and erase operations. The code can include boot codeand control code (set of instructions). The boot code is software thatinitializes the controller during a booting or startup process andenables the controller to access the memory structure. The code can beused by the controller to control one or more memory structures. Uponbeing powered up, the processor 122 c fetches the boot code from the ROM122 a or storage device 126 a for execution, and the boot codeinitializes the system components and loads the control code into theRAM 122 b. Once the control code is loaded into the RAM, it is executedby the processor. The control code includes drivers to perform basictasks such as controlling and allocating memory, prioritizing theprocessing of instructions, and controlling input and output ports.

Other types of non-volatile memory in addition to NAND flash memory canalso be used.

Semiconductor memory devices include volatile memory devices, such asdynamic random access memory (“DRAM”) or static random access memory(“SRAM”) devices, non-volatile memory devices, such as resistive randomaccess memory (“ReRAM”), electrically erasable programmable read onlymemory (“EEPROM”), flash memory (which can also be considered a subsetof EEPROM), ferroelectric random access memory (“FRAM”), andmagnetoresistive random access memory (“MRAM”), and other semiconductorelements capable of storing information. Each type of memory device mayhave different configurations. For example, flash memory devices may beconfigured in a NAND or a NOR configuration.

The memory devices can be formed from passive and/or active elements, inany combinations. By way of non-limiting example, passive semiconductormemory elements include ReRAM device elements, which in some embodimentsinclude a resistivity switching storage element, such as an anti-fuse orphase change material, and optionally a steering element, such as adiode or transistor. Further by way of non-limiting example, activesemiconductor memory elements include EEPROM and flash memory deviceelements, which in some embodiments include elements containing a chargestorage region, such as a floating gate, conductive nanoparticles, or acharge storage dielectric material.

Multiple memory elements may be configured so that they are connected inseries or so that each element is individually accessible. By way ofnon-limiting example, flash memory devices in a NAND configuration (NANDmemory) typically contain memory elements connected in series. A NANDstring is an example of a set of series-connected transistors comprisingmemory cells and select gate transistors.

A NAND memory array may be configured so that the array is composed ofmultiple strings of memory in which a string is composed of multiplememory elements sharing a single bit line and accessed as a group.Alternatively, memory elements may be configured so that each element isindividually accessible, e.g., a NOR memory array. NAND and NOR memoryconfigurations are exemplary, and memory elements may be otherwiseconfigured.

The semiconductor memory elements located within and/or over a substratemay be arranged in two or three dimensions, such as a two dimensionalmemory structure or a three dimensional memory structure.

In a two dimensional memory structure, the semiconductor memory elementsare arranged in a single plane or a single memory device level.Typically, in a two dimensional memory structure, memory elements arearranged in a plane (e.g., in an x-y direction plane) which extendssubstantially parallel to a major surface of a substrate that supportsthe memory elements. The substrate may be a wafer over or in which thelayer of the memory elements are formed or it may be a carrier substratewhich is attached to the memory elements after they are formed. As anon-limiting example, the substrate may include a semiconductor such assilicon.

The memory elements may be arranged in the single memory device level inan ordered array, such as in a plurality of rows and/or columns.However, the memory elements may be arrayed in non-regular ornon-orthogonal configurations. The memory elements may each have two ormore electrodes or contact lines, such as bit lines and word lines.

A three dimensional memory array is arranged so that memory elementsoccupy multiple planes or multiple memory device levels, thereby forminga structure in three dimensions (i.e., in the x, y and z directions,where the z direction is substantially perpendicular and the x and ydirections are substantially parallel to the major surface of thesubstrate).

As a non-limiting example, a three dimensional memory structure may bevertically arranged as a stack of multiple two dimensional memory devicelevels. As another non-limiting example, a three dimensional memoryarray may be arranged as multiple vertical columns (e.g., columnsextending substantially perpendicular to the major surface of thesubstrate, i.e., in the y direction) with each column having multiplememory elements. The columns may be arranged in a two dimensionalconfiguration, e.g., in an x-y plane, resulting in a three dimensionalarrangement of memory elements with elements on multiple verticallystacked memory planes. Other configurations of memory elements in threedimensions can also constitute a three dimensional memory array.

By way of non-limiting example, in a three dimensional NAND memoryarray, the memory elements may be coupled together to form a NAND stringwithin a single horizontal (e.g., x-y) memory device level.Alternatively, the memory elements may be coupled together to form avertical NAND string that traverses across multiple horizontal memorydevice levels. Other three dimensional configurations can be envisionedwherein some NAND strings contain memory elements in a single memorylevel while other strings contain memory elements which span throughmultiple memory levels. Three dimensional memory arrays may also bedesigned in a NOR configuration and in a ReRAM configuration.

Typically, in a monolithic three dimensional memory array, one or morememory device levels are formed above a single substrate. Optionally,the monolithic three dimensional memory array may also have one or morememory layers at least partially within the single substrate. As anon-limiting example, the substrate may include a semiconductor such assilicon. In a monolithic three dimensional array, the layersconstituting each memory device level of the array are typically formedon the layers of the underlying memory device levels of the array.However, layers of adjacent memory device levels of a monolithic threedimensional memory array may be shared or have intervening layersbetween memory device levels.

Then again, two dimensional arrays may be formed separately and thenpackaged together to form a non-monolithic memory device having multiplelayers of memory. For example, non-monolithic stacked memories can beconstructed by forming memory levels on separate substrates and thenstacking the memory levels atop each other. The substrates may bethinned or removed from the memory device levels before stacking, but asthe memory device levels are initially formed over separate substrates,the resulting memory arrays are not monolithic three dimensional memoryarrays. Further, multiple two dimensional memory arrays or threedimensional memory arrays (monolithic or non-monolithic) may be formedon separate chips and then packaged together to form a stacked-chipmemory device.

Associated circuitry is typically required for operation of the memoryelements and for communication with the memory elements. As non-limitingexamples, memory devices may have circuitry used for controlling anddriving memory elements to accomplish functions such as programming andreading. This associated circuitry may be on the same substrate as thememory elements and/or on a separate substrate. For example, acontroller for memory read-write operations may be located on a separatecontroller chip and/or on the same substrate as the memory elements.

One of skill in the art will recognize that this technology is notlimited to the two dimensional and three dimensional exemplarystructures described but covers all relevant memory structures withinthe spirit and scope of the technology as described herein and asunderstood by one of skill in the art.

FIG. 2A depicts a top view of example word line layers 202 and 204 in aU-shaped NAND embodiment, as an example implementation of BLK0 in FIG.1A. In a 3D stacked memory device, memory cells are formed along memoryholes which extend through alternating conductive and dielectric layersin a stack. The memory cells are typically arranged in NAND strings.Each conductive layer can include one or more word line layers. A wordline layer is an example of a word line.

The view is of a representative layer among the multiple WLLs in astack. Referring also to FIG. 2C, the stack includes alternatingdielectric and conductive layers. The dielectric layers include DL0 toDL16 and may be made of SiO2, for instance. The conductive layersinclude a back gate layer (BGL), data word line layers WLL0 to WLL10,dummy word line layers DWLL1 and DWLL2, and select gate layers SGL1 andSGL2. The word line layers are conductive paths to control gates of thememory cells at the layer. Moreover, each select gate layer maycomprises conductive lines to select gate transistors (e.g., SGD and/orSGS transistors).

As mentioned, a dummy memory cell, also referred to as a non-data memorycell, does not store data, while a data memory cell is eligible to storedata. Thus, data memory cells may be programmed to store write data.After a block is erased, all data memory cells are in the erased state.As some word lines are programmed, the corresponding data memory cellsstore data while other data memory cells do not store data. As aremainder of the block is programmed, all data memory cells typicallystore data.

The word line layers of FIG. 2A may represent any one of the word linelayers in FIG. 2C. These conductive layers may include dopedpolysilicon, metal such as tungsten or metal silicide, for instance. Anexample voltage of 5-10 V may be applied to the back gate to maintain aconductive state which connects the drain- and source-side columns.

For each block, each conductive layer may be divided into two word linelayers 202 and 204 which are insulated from one another by a slit 206.The slit is formed by etching a void which extends vertically in thestack, typically from an etch stop layer at the bottom to at least a toplayer of the stack, then filling the slit with insulation. This is anexample of the type of etching which can result in the accumulation ofcharges in the top conductive layer of the stack. The slit 206 is asingle continuous slit which extends in a zig-zag pattern in the block.This approach can provide greater flexibility in controlling the memorycells since the WLLs can be driven independently.

Each block includes vertically-extending memory holes or pillars whichextend vertically in the stack, and comprise a column of memory cellssuch as in a NAND string. Each circle represents a memory hole or amemory cell associated with the word line layer. Example columns ofmemory cells along a line 220 include C0 to C11. Columns C0, C3, C4, C7,C8 and C11 represent the drain side columns of respective NAND strings.Columns C1, C2, C5, C6, C9 and C10 represent the source side columns ofrespective NAND strings. The figure represents a simplification, as manymore rows of memory holes will typically be used, extending to the rightand left in the figure. Also, the figures are not necessarily to scale.The columns of memory cells can be arranged in subsets such assub-blocks.

Further, the NAND strings are arranged in sets, where each NAND stringin a set has an SGD transistor with a common control gate voltage. Seealso FIG. 2B. Regions 201, 203, 205, 207, 208 and 210 each represent aset of NAND strings, or a set of memory cells in a word line layer. Forexample, region 210 includes NAND strings NS0, . . . , NS0-14. Aprogramming operation can involve one set of NAND strings. Each NANDstring in a set can be associated with a respective bit line which isindependently controlled to allow or inhibit programming.

The drawings are not to scale and do not show all memory columns. Forexample, a more realistic block might have twelve memory columns in they direction as shown, but a very large number such as 32 k memorycolumns in the x direction, for a total of 384,000 memory columns in ablock. With U-shaped NAND strings, 192 k NAND strings are provided inthis example. With straight NAND strings, 384,000 NAND strings areprovided in this example. Assuming there are twenty-four memory cellsper column, there are 384,000×24=9,216,000 memory cells in the set.

FIG. 2B depicts a top view of example select gate layer portions,consistent with FIG. 2A. In one approach, the select gate layer 215 isdifferent than a WLL in that a separate SGD layer portion or line, isprovided for each set of NAND strings. That is, each single row of SGDtransistors extending in the x direction is separately controlled. Inother words, the control gates of the SGD transistors in each set ofNAND strings are commonly controlled.

Further, an SGS layer portion or line is provided for a pair of rows ofSGS transistors extending in the x direction, in one approach, foradjacent sets of NAND strings. Optionally, additional slits are used sothat a separate SGS layer portion is provided for a single row of SGStransistors extending in the x direction. Thus, the control gates of theSGS transistors in a pair of rows of SGS transistors, or in a single rowof SGS transistors, are also commonly controlled.

The SGS and SGD layer portions are created due to slits 239, 240, 241,242, 243, 245, 247 and 248. The slits extend partway down in the stackas depicted by example slit 241 in FIG. 2C. Regions 227, 228, 229, 232,233 and 237 represent SGD transistors in SGD lines 216, 218, 219, 223,224 and 226, respectively. Regions 253 and 254, 255 and 257, and 258 and259 represent SGS transistors in SGS lines 217, 221 and 225,respectively. Regions 255 and 257, 258 and 259, represent SGStransistors in SGS layer portions 221 and 225, respectively. The portion209 from FIG. 2A is repeated for reference.

The select gate transistors are associated with NAND strings NS0-NS5.

FIG. 2C depicts an embodiment of a stack 231 showing a cross-sectionalview of the portion 209 of FIG. 2A, along line 220, where select gatelayers SGL1 and SGL2 are provided. In this case, the slit extends downto SGL2, so that two separate layers of select gate transistors areformed in each column of each NAND string. The stack has a top 287 and abottom 238.

The conductive layers of the select gates can have a same height(channel length) as the conductive layers of the memory cells, in oneapproach. This facilitates the fabrication of the memory device. In acolumn, the individual select gate transistors together are equivalentto one select gate transistor having a channel length which is the sumof the channel lengths of the individual select gate transistors.Further, in one approach, select gate transistors in a column (e.g., inlayers SGL1 and SGL2) are connected and received a common voltage duringoperations. The SGS transistors can have a similar construction as theSGD transistors. Further, the SGS and SGD transistors can have a similarconstruction as the memory cell transistors.

The substrate may be p-type and can provide a ground which is connectedto the top select gate layer, in one approach. A via 244 connects adrain side of C0 and NS0 to a bit line 288. A via 262 connects a sourceside of C1 and NS0 to a source line 289. Back gates 263, 264, 265 and266 are provided in NS0, NS1, NS2 and NS3, respectively.

Regions D1, D2, D3 and D4 represent SGD transistors and regions S1, S2,S3 and S4 represent SGS transistors in SGL1.

Generally, a control gate layer can refer to a word line layer, which isconnected to dummy memory cells or data memory cells, or a select gatelayer, which is connected to select gate transistors.

FIG. 2D depicts an alternative view of the select gate layers and wordline layers of the stack 231 of FIG. 2C. The SGL layers SGL1 and SGL2each includes parallel rows of select gate lines associated with thedrain-side (shown by solid lines) or source-side (shown by dotted lines)of a set of NAND strings. For example, SGL1 includes drain-side selectgate lines 216, 218, 219, 223, 224 and 226 and source-side select gatelines 217, 221 and 225, consistent with FIG. 2B. Each select gate linecan be independently controlled, in one approach.

Below, the SGL layers are the word line layers. Each word line layerincludes a drain-side word line connected to memory cells on adrain-side of a NAND string (the half of a NAND string between the backgate and the drain end) and a source-side word line connected to memorycells on a source-side of a NAND string (the half of a NAND stringbetween the back gate and the source end). For example, DWLL1, DWLL2,WLL10, WLL9 and WLL8 include drain-side word lines 270 d, 271 d, 272 d,273 d and 274 d, respectively, and source-side word lines 270 s, 271 s,272 s, 273 s and 274 s, respectively.

WLL3, WLL2, WLL1 and WLL0 include drain-side word lines 275 d, 276 d,277 d and 278 d, respectively, and source-side word lines 275 s, 276 s,277 s and 278 s, respectively. Each word line can be controlledindependently, in one approach.

In an example programming operation, the source-side word line 272 s isa first programmed word line and a drain-side word line 272 d is a finalprogrammed word line in a block.

FIG. 3A depicts a top view of an example word line layer 304 of theblock BLK0 of FIG. 1A, in a straight NAND string embodiment. In thisconfiguration, a NAND string has only one column, and the source-sideselect gate is on the bottom of the column instead of on the top, as ina U-shaped NAND string. Moreover, a given level of a block has one WLLwhich is connected to each of the memory cells of the layer.Insulation-filled slits 346, 347, 348, 349 and 350 can also be used inthe fabrication process to provide structural support for the stack. Adashed line 305 extends through columns C12-C17. A cross-sectional viewalong line 305 of portion 307 is shown in FIG. 3C.

Regions 340, 341, 342, 343, 344 and 345 represent the memory cells (ascircles) of respective sets of NAND strings. For example, region 340represents memory cells in NAND strings NS0A, NS0A-14. Additional NANDstrings include NS1A, NS2A, NS3A, NS4A and NS5A. A programming operationfor a block can involve programming one set of NAND strings at a time,one word line layer at a time. For example, the memory cells of the NANDstring set of region 340 may be programmed first, followed by the memorycells of the NAND string set of region 341, and so forth. Similarly, aread operation for a block can involve sensing one set of NAND stringsat a time, while a control gate voltage is applied to a selected wordline layer and pass voltages are applied to remaining word line layers.

Alternatively, the layer 304 represents an SGS layer, in which case eachcircle represents an SGS transistor.

FIG. 3B depicts a top view of an example SGD layer 362, consistent withFIG. 3A. Slits 357, 358, 359, 360 and 361 divide the SGD layer intoportions 363, 364, 365, 366, 367 and 368. Each portion connects the SGDtransistors in a set of NAND strings. For example, SGD layer portion 363or line connects the SGD transistors in the set of NAND strings NS0A toNS0A-14. Regions 351, 352, 353, 354, 355 and 356 represent the SGDtransistors (as circles) of respective sets of NAND strings in the SGDlayer portions 363, 364, 365, 366, 367 and 368, respectively. Theportion 307 from FIG. 3A is also repeated. The select gate transistorsare associated with NAND strings NS0A-NS5A.

Bit lines BLx are also depicted which connect to the top portions of thememory holes. During programming, each portion 363, 364, 365, 366, 367and 368 is programmed separately and the bit line voltages are set at aninhibit level (e.g., 2-3 V) or a program level (e.g., 0 V).

FIG. 3C depicts an embodiment of a stack 376 showing a cross-sectionalview of the portion 307 of FIG. 3A, along line 305. Two SGD layers, twoSGS layers and four dummy word line layers DWLL1 a, DWLL1 b, DWLL2 a andDWLL2 b are provided.

Columns of memory cells corresponding to NAND strings NS0A-NS3A aredepicted in the multi-layer stack. The stack includes a substrate 101,an insulating film 250 on the substrate, and a portion of a source lineSL0A. Additional straight NAND strings in a SGD line subset extendbehind the NAND strings depicted in the cross-section, e.g., along thex-axis. NS0A has a source end SEa and a drain end DEa. The slits 346,347 and 348 from FIG. 3A are also depicted. A portion of the bit lineBL0A is also depicted. A conductive via 373 connects DEa to BL0A. Thecolumns are formed in memory holes MH0-MH3. The memory holes arecolumnar and extend at least from a top 370 to a bottom 371 of thestack.

The source line SL0A is connected to the source ends of each NANDstring. SL0A is also connected to other sets of memory strings which arebehind these NAND strings in the x direction.

Control gate layers (e.g., data word line layers WLL0-WLL10 and dummyword line layers DWLL1 a, DWLL1 b, DWLL2 a and DWLL2 b) and dielectriclayers (e.g., DL0-DL19), are arranged alternatingly in the stack. SGStransistors 369, 372, 374 and 375 are formed in the SGS1 layer.

A region 246 of the stack is shown in greater detail in FIG. 4A. SGDtransistors 480, 484, 485 and 486 are provided by the dashed-lineregions.

FIG. 3D depicts an alternative view of the select gate layers and wordline layers of the stack 376 of FIG. 3C. The SGD layers SGD1 and SGD2each includes parallel rows of select gate lines associated with thedrain-side of a set of NAND strings. For example, SGD1 includesdrain-side select gate lines 363, 364, 365, 366, 367 and 368, consistentwith FIG. 3B. Each select gate line can be independently controlled, inone approach.

Below the SGD layers are the word line layers. Each word line layerrepresents a word line, in one approach, and is connected to a set ofmemory cells at a given height in the stack. For example, DWLL1 a, DWLL1b, WLL10, WLL9, WLL8 and WLL7 represent word lines 399, 398, 397, 396,395 and 394, respectively. WLL2, WLL1, WLL0, DWLL2 b and DWLL2 arepresent word lines 393, 392, 391, 390 and 389, respectively. Each wordline can be controlled independently, in one approach.

Below the word line layers are the SGS layers. The SGS layers SGS1 andSGS2 each includes parallel rows of select gate lines associated withthe source-side of a set of NAND strings. For example, SGS1 includessource-side select gate lines 380, 381, 382, 383, 384 and 385. Eachselect gate line can be independently controlled, in one approach.

In an example programming operation, the source-side word line 391 is afirst programmed word line and a drain-side word line 397 is a finalprogrammed word line in a block.

FIG. 4A depicts a top view of an example word line layer 400 of theblock BLK0 of FIG. 1A, in another straight NAND string embodiment. Thisapproach provides rows of memory holes in a staggered pattern toincrease the density of the memory holes. The word line layer is dividedinto regions 406, 407, 408 and 409 which are each connected by aconnector 413. The connector, in turn, is connected to a voltage driverfor the word line layer. The region 406 has example memory holes 410 and411 along a line 412. See also FIG. 4C. Metal-filled slits 401, 402,403, 404 and 405 (e.g., metal interconnects) may be located between andadjacent to the edges of the regions 406-409. The metal-filled slitsprovide a conductive path from the bottom of the stack to the top of thestack. For example, a source line at the bottom of the stack may beconnected to a conductive line above the stack, where the conductiveline is connected to a voltage driver in a peripheral region of thememory device. The metal-filled slits may be provided from the slitswhich are used during the fabrication, prior to being filled with metal,for tasks such as removing sacrificial material of the control gatelayers.

FIG. 4B depicts a top view of an example SGD layer 420, consistent withFIG. 4A. The SGD layer is divided into regions 426, 427, 428 and 429.Each region can be connected to a respective voltage driver. The region426 has the example memory holes 410 and 411 along a line 412 a. Seealso FIG. 4C. A number of bit lines extend above the memory holes andare connected to the memory holes as indicated by the “X” symbols. Anexample bit line 430 is connected to a set of memory holes whichincludes the memory hole 411. The metal-filled slits 401, 402, 403, 404and 405 from FIG. 4A are also depicted, as they extend verticallythrough the stack.

FIG. 4C depicts an embodiment of a stack 440 showing a cross-sectionalview along line 412 of FIG. 4A and line 412 a of FIG. 4B. Two SGDlayers, two SGS layers and four dummy word line layers DWLL1 a, DWLL1 b,DWLL2 a and DWLL2 b are provided. Columns of memory cells correspondingto NAND strings NS1B and NS2B are depicted in the multi-layer stack. Thestack includes a substrate 101, an insulating film 250 on the substrate,and a portion of a source line SL0A. NS1B has a source end SEb at abottom 444 of the stack and a drain end Deb at a top 443 of the stack.The metal-filled slits 401 and 402 from FIGS. 4A and 4B are alsodepicted. A portion of the bit line BLx is also depicted. A conductivevia 441 connects DEb to BLx. A region 442 of the stack is shown ingreater detail in FIGS. 4E and 4F.

FIG. 4D depicts an alternative view of the select gate layers and wordline layers of the stack 440 of FIG. 4C. The SGD layers SGD1 and SGD2each includes parallel rows of select gate lines associated with thedrain-side of a set of NAND strings. For example, SGD1 includesdrain-side select gate regions 426, 427, 428 and 429 consistent withFIG. 4B. Each select gate line can be independently controlled, in oneapproach.

Below the SGD layers are the drain-side dummy word line layers. Eachdummy word line layer represents a word line, in one approach, and isconnected to a set of dummy memory cells at a given height in the stack.For example, DWLL1 a comprises word line layer portions 450, 451, 452and 453.

Below the dummy word line layers are the data word line layers. Forexample, WLL10 comprises word line layer portions 406, 407, 408 and 409.

Below the data word line layers are the source-side dummy word linelayers.

Below the source-side dummy word line layers are the SGS layers. The SGSlayers SGS1 and SGS2 each includes parallel rows of select gate linesassociated with the source-side of a set of NAND strings. For example,SGS1 includes source-side select gate lines 454, 455, 456 and 457. Eachselect gate line can be independently controlled, in one approach. Or,the select gate lines can be connected and commonly controlled.

FIG. 4E depicts a view of the region 246 of FIG. 3C or the region 442 ofFIG. 4C1, where a blocking oxide layer is provided along the sidewall ofthe memory hole. SGD transistors 480 and 481 are provided above dummymemory cells 482 and 483 and a data memory cell MC. A number of layerscan be deposited along the sidewalls (SW) of the memory hole (MHx)and/or within each word line layer, e.g., using atomic layer deposition.For example, each column (e.g., the pillar which is formed by thematerials within a memory hole) can include a charge-trapping layer orfilm (CTL) 463 such as SiN or other nitride, a tunneling material (TM)464, a polysilicon body or channel (CH) 465, and a dielectric core (DC)466. A word line layer can include a blocking oxide (BOx) 470, a blockhigh-k material 460, a metal barrier (MB) 461, and a conductive metalsuch as W 462 as a control gate. For example, control gates 490, 491,492, 493 and 494 are provided. In another approach, all of these layersexcept the metal are provided in the memory hole. Additional pillars aresimilarly formed in the different memory holes. A pillar can form acolumnar active area (AA) of a NAND string.

When a memory cell is programmed, electrons are stored in a portion ofthe CTL which is associated with the memory cell. These electrons aredrawn into the CTL from the channel, and through the tunneling material(TM). The Vth of a memory cell is increased in proportion to the amountof stored charge. During an erase operation, the electrons return to thechannel.

Each of the memory holes can be filled with a plurality of annularlayers comprising a blocking oxide layer, a charge trapping layer, atunneling material and a channel layer. A core region of each of thememory holes is filled with a body material, and the plurality ofannular layers are between the core region and the WLLs in each of thememory holes.

In some cases, the tunneling material 464 can comprise multiple layerssuch as in an oxide-nitride-oxide configuration.

In this example, the charge-trapping material has been removed from theSGD transistors 480 and 481 and from the dummy memory cells 482 and 483,but remains in the data memory cell MC. For example, a region 480 ashows where the charge-trapping material of the SGD transistor 480 wasremoved, and a region MCa shows where the charge-trapping material ofthe data memory cell MC was removed.

One or more of the control gate layers SGD1, SGD2, DWLL1 a and DWLL1 bcan be considered to be a control gate layer for a first transistor(e.g., an SGD transistor 480 or 481 or a dummy memory cell 482 or 483above control gate layers (e.g., WLL0-WLL10) for data memory cells(e.g., MC). The first transistor could be a drain-side select gatetransistor, a source-side select gate transistor, a drain-side dummymemory cell and/or source-side dummy memory cell.

FIG. 4F depicts a view of the region 246 of FIG. 3C or the region 442 ofFIG. 4C1, where a blocking oxide layer is provided within the controlgate layers. For example, the BOx layer 471 is provided within SGD1. Inthis example, the charge-trapping material has been removed from the SGDtransistors 480 and 481 and from the dummy memory cells 482 and 483, butremains in the data memory cell MC. For example, a region 480 b showswhere the charge-trapping material of the SGD transistor 480 wasremoved, and a region MCb shows where the charge-trapping material ofthe data memory cell MC remains in the memory device and is not removed.The memory hole is MHy.

FIG. 4G depicts an overview of the fabrication processes of FIG. 5. Theprocess includes removing a sacrificial material and a charge-trappingmaterial in a second set of control gate layers in a stack, withoutremoving a sacrificial material and a charge-trapping material in afirst set of control gate layers in a stack (step 498), followed byremoving a sacrificial material without removing a charge-trappingmaterial from the first set of control gate layers in the stack (step499). This process can be carried out in various implementation. Exampleimplementations are provided in connection with FIG. 5 and the followingfigures.

FIG. 5 depicts a fabrication process for a 3D stack in a memory devicein which a charge-trapping material is removed from select gatetransistors and/or dummy memory cells. For conciseness, a number ofoptions in the fabrication process are depicted. Control gate (CG)options involve the composition of the sacrificial material in thedifferent control gate layers of the stack. For instance, CG option 1 or2 may be used. BOx options involve the location of a blocking oxidelayer in the stack. BOx option A and/or B may be used. The steps areillustrated in connection with the following figures.

Step 500 involves forming a stack comprising alternating: a) controlgate (CG) layers of sacrificial material and b) dielectric layers. Instep 500 a (CG option 1), the sacrificial material is different in: a)the CG layers of the select gate transistors and/or the dummy memorycells compared to b) the CG layers of the data memory cells. Thedifferent sacrificial materials have different etch rates when subjectto an etchant. For example, polysilicon can be used for the CG layersfor the select gate transistors and/or the dummy memory cells, andsilicon nitride (SiN) can be used for the CG layers for the data memorycells. In step 500 b (CG option 2), the sacrificial material can besubstantially the same in the CG layers of the select gate transistors,the dummy memory cells and the data memory cells. For example, SiN canbe used.

Step 501 involves forming memory holes in the stack. For example,reactive ion etching, a type of dry etching, may be used. In step 502(BOx option A), a blocking oxide layer is deposited on the sidewalls ofthe memory holes. Subsequently, step 503 involves depositing acharge-trapping material (e.g., SiN, hafnium oxide, aluminum oxide orother material), a tunneling material (e.g., oxide) and a channelmaterial (e.g., polysilicon) on the sidewalls of the memory holes. Step504 involves etching through the materials at the bottom of the memoryholes to allow the channel material to communicate with the source line,depositing a core filler and performing CMP.

Step 505 involves etching a slit (one or more slits) in the stack. Inone approach, the stack is etched from its top to its bottom so that theslit extend the full height of the stack. In another approach, step 505involves a partial etch of the stack which is followed by a second etchat step 509 b. A slit is an example of a void in the stack and can havea trench shape, in one example.

Step 506 a (CG option 2) involves depositing a protective layer in theslit and step 506 (CG option 2) involves etching the protective layerdown to a specified height in the stack, between the CG layers of theselect gate transistors and/or the dummy memory cells and the CG layersof the data memory cells. For example, the height can be between the CGlayers of the select gate transistors and/or the dummy memory cells atthe drain-side of each NAND string and the CG layers of the data memorycells. An example of a material for the protective layer is oxide. Whenremoving the sacrificial material in the open which are not covered bythe protective layer, the oxide can prevent the sacrificial materialwhich is covered by the protective layer from being etched away.

Step 507 involves using the slit to remove sacrificial material of theCG layers of select gate transistors and/or dummy memory cells, therebyforming voids in the CG layers of the select gate transistors and/ordummy memory cells. This step can include providing an etchant in theslit.

Step 508 (BOx option A) involves using the slit and the voids in the CGlayers of the select gate transistors and/or dummy memory cells toremove portions of the BOx layer. This step can include providing anetchant in the slit.

Step 509 involves using the slit and the voids in the CG layers of theselect gate transistors and/or dummy memory cells to remove portions ofthe associated charge-trapping material. This step can include providingan etchant in the slit. Once the sacrificial material is removed, aportion of the first layer of material which was deposited along thesidewall of the memory hole is exposed. In some cases, this is theblocking oxide layer. The etch chemistry can be varied during theetching process. For example, an etchant such as diluted hydrofluoric(DHF) acid is suitable for etching oxide, while phosphoric acid issuitable for etching nitride and TMAH is suitable for etchingpolysilicon. Thus, TMAH can be supplied to remove a polysiliconsacrificial layer, then DHF acid can be supplied to remove a blockingoxide material, then phosphoric acid can be supplied to remove a nitridecharge-trapping material. The blocking oxide layer can be relativelythin, and can act as an etch stop to the lateral etching of thepolysilicon sacrificial material. If the tunneling material (e.g.,oxide) is also to be removed, such as to access the channel material forlateral doping, DHF acid can be supplied again via the slit in theetching process.

The etchants which are provided in the slit and travel horizontally toetch away the sacrificial material and the charge-trapping material cancomprises a chemical dry etchant. That is, vapor phase etching can beused.

With the removal of the charge-trapping material, the select gatetransistors and the dummy memory cells become transistors in which theblocking oxide is a gate oxide. These transistors are not charge-storingtransistors and do not comprise a charge-storing material.

Step 509 a involves an option to remove portions of the tunnelingmaterial and laterally dope the channel material, e.g., using a dry gas.A heating step may also be used to active the dopants.

Step 509 b involves an option to provide a deeper etch of the slit, tothe bottom of the stack. In this case, the etching of the slit at step505 is a partial etch of the stack, down to a specified height. Forexample, the specified height can be between a bottommost control gatelayer of the control gate layers for the dummy memory cells and/or theselect gate transistors and a topmost control gate layer of the controlgate layers for the data memory cells. Essentially, the transistors(e.g., select gate transistors and/or dummy memory cells) above thespecified height have their charge-trapping material removed and thetransistors below the specified height do not have their charge-trappingmaterial removed. The etching of the slit in step 509 b can then be anetch from the specified height to a bottom of the stack, through aremaining portion of the stack.

Generally, etching the slits twice is feasible since the slits tend tohave a wider cross-section compared to the memory holes, for example.Although, there is an additional expense in terms of a secondlithography.

Step 510 (CG option 2) involves etching away the remaining portion ofthe protective layer.

Step 511 involves using the slit to remove sacrificial material of theCG layers of the data memory cells, thereby forming voids in the CGlayers of the data memory cells. For example, phosphoric acid can besupplied to remove the SiN sacrificial material, DHF acid can besupplied to remove a blocking oxide material, then phosphoric acid canbe supplied again to remove a nitride charge-trapping material.

When the first sacrificial material is being etched in the control gatelayers for the dummy memory cells and/or the select gate transistors,the second sacrificial material in the control gate layers for the datamemory cells generally is not significantly etched. This is true becausea first etchant is used which is more selective of the first sacrificialmaterial than the second sacrificial material. That is, the firstetchant causes a higher etch rate for the first sacrificial materialthan the second sacrificial material. A second etchant is used to etchthe second sacrificial material in the control gate layers for the datamemory cells. The second etchant is used which is more selective of thesecond sacrificial material than the dielectric. Similarly, when thefirst and second sacrificial materials are being etched, the dielectriclayers are not significantly etched.

For example, the first sacrificial material can comprise polysilicon,the second sacrificial material can comprise SiN, the first etchant cancomprise tetra methyl ammonium hydroxide (TMAH) and the second etchantcan comprise phosphoric acid.

Step 512 (BOx option B) involves using the slit to deposit a BOx layerin the CG layers of the select gate transistors and/or dummy memorycells and in the voids in the CG layers of the data memory cells. Step513 involves using the slit to deposit a metal in the voids in the CGlayers of the select gate transistors and/or dummy memory cells and inthe voids in the CG layers of the data memory cells. This depositiontypically fills the voids and all or most of the slit with metal. Step513 also includes further processing of the slit, such as etching awaythe metal in the slit, depositing an insulating layer on the sidewallsof the slit, etching through the insulating layer at the bottom of theslit and depositing metal in the slit. Further processing includes theformation of structures above the stack including control lines such asbit lines and vias to the control lines.

Step 514 involves an option to dope the channel material using ionimplantation from the top of the stack. Example p-type dopants includeBoron, Arsenic or Phosphorus which cause the channel material to becomen-type and therefore have a higher Vth. A heating step can also be usedto activate the implanted dopants. For example, rapid thermal annealingat 900-1000 C for 10-30 seconds may be used. The heating generatesvacancies which facilitate the movement of the dopants. The ionimplantation can be controlled to provide a desired dopant concentrationprofile along the channel material.

A further option is to provide a different level of lateral doping forthe drain-side select gate transistors compared to the drain-side dummymemory cells. In this case, the techniques described herein can bemodified to first expose the channel portions of the drain-side selectgate transistors to the slit while the channel portions of the remainingtransistors are not exposed to the slit. The drain-side select gatetransistors can be laterally doped to a first dopant concentration, forexample. The process then exposes the channel portions of the drain-sidedummy memory cells to the slit while the channel portions of theremaining transistors are not exposed to the slit. The drain-side dummymemory cells can be laterally doped to a second dopant concentration,for example. The process then removes the sacrificial material of theremaining control gate layers.

In one possible implementation, a first sacrificial material is used forthe drain-side select gate transistors, a second sacrificial material isused for the drain-side dummy memory cells and a third sacrificialmaterial is used for the remaining transistors, where each of thesesacrificial materials can be selectively etched. The first sacrificialmaterial is etched to remove the associated charge-trapping material anddope the associated channel portions. At another time, the secondsacrificial material is etched to remove the associated charge-trappingmaterial and dope the associated channel portions. At another time, thethird sacrificial material is etched. For example, the third sacrificialmaterial can be carbon. One option of etchant for carbon is H2SO4(sulfuric acid):H2O2 (hydrogen peroxide) in a 3:1 ratio. The othersacrificial materials can be polysilicon and SiN as before.

Various examples implementations of the fabrication process arediscussed below in connection with FIG. 6A-9B, which are generallyconsistent with the structure of FIG. 4C.

FIG. 6A depicts a semiconductor structure 600 comprising a stack ofalternating control gate layers and dielectric layers in accordance withsteps 500 and 500 a of FIG. 5. An example dielectric material 601 (e.g.,oxide) is in DL19. An example first sacrificial material (e.g.,polysilicon) is provided in SGD1, SGD2, DWLL1 a and DWLL1 b. Forexample, regions 602 and 603 of the first sacrificial material areprovided in SGD1 and DWLL1 a, respectively. An example secondsacrificial material (e.g., SiN) is provided in WLL0-WLL10. For example,a region 604 of the second sacrificial material is provided in WLL10.WLL10 is the topmost CG layer of the CG layers for the data memorycells.

In this example, the second sacrificial material is also provided forthe source-side select gate layers and dummy memory cell layers.Generally, it is acceptable to leave in the charge-trapping layer forthese layers since the transistors of the drain-side layers tend to bemore important in the operation of the NAND string. Moreover, thetransistors of the source-side layers are less susceptible to havingtheir Vth increased. Alternatively, it is possible to provide the firstsacrificial material for the drain-side layers as well (see FIG. 6B) toallow subsequent removal of the charge-trapping layer for these layersas well.

FIG. 6B depicts a semiconductor structure 605 comprising a stack ofalternating control gate layers and dielectric layers in accordance withsteps 500 and 500 a of FIG. 5, in an option where source-side controlgate layers also have a different sacrificial material than the controlgate layers of the data memory cells. This is a modification of thesemiconductor structure of FIG. 6A. The example first sacrificialmaterial (e.g., polysilicon) is also provided in SGS1, SGS2, DWLL2 a andDWLL2 b. For example, regions 609 and 606 of the first sacrificialmaterial are provided in SGS1 and DWLL2 a, respectively. A region 607 ofthe second sacrificial material is provided in WLL0. WLL0 is thebottommost CG layer of the CG layers for the data memory cells.

FIG. 6C depicts a semiconductor structure 610 obtained by processing thesemiconductor structure of FIG. 6A in accordance with step 501 of FIG.5. Memory holes 611 and 612 are etched in this example.

FIG. 6D depicts a semiconductor structure 620 obtained by processing thesemiconductor structure of FIG. 6C in accordance with step 503 of FIG.5. A number of films are deposited in a blanket deposition, including ablocking oxide layer 621, a charge-trapping material 622, a tunnelingoxide layer 623 and a channel material 624.

FIG. 6E depicts a semiconductor structure 630 obtained by processing thesemiconductor structure of FIG. 6D in accordance with step 504 of FIG.5. After openings 631 and 632 are formed at the bottom of the memoryholes to allow the channel material to communicate with the source line,a core filler 633 is blanket deposited over the other layers of thesemiconductor structure of FIG. 6D. CMP is performed to planarize thetop surface of the stack. The remaining portions of the materials alongthe sidewalls of the memory holes are depicted, including the blockingoxide layer 621 a, the charge-trapping material 622 a, the tunnelingmaterial 623 a and the channel material 624 a.

In this and other figures, the materials along the sidewalls of a memoryholes appear as separate films but are actually part of a single hollowcylinder or tube.

FIG. 6F depicts a semiconductor structure 640 obtained by processing thesemiconductor structure of FIG. 6E in accordance with step 505 of FIG.5. Slits 641 and 642 are formed. In this and other figures, forconciseness, the width of the slit is depicted as being similar to thewidth of the memory holes. In practice, the width of the slit istypically larger than the width of the memory holes to facilitate thedeposition of etchants and other materials via the slit. Also, note thatthe use of dummy memory cells is optional, the number of control gatelayers can be one or more for the drain-side and source-side select gatetransistors and for the dummy memory cells, when used. Further, theheight of the different control gate layers can be uniform as depictedor varied.

FIG. 6G depicts a semiconductor structure 650 obtained by processing thesemiconductor structure of FIG. 6F in accordance with step 507 of FIG.5, in an option in which the sacrificial material is removed for thedrain-side select gate layers and dummy memory cells. Voids 651, 652,653 and 654 are formed in SGD1, SGD2, DWLL1 a and DWLL1 b, respectively.Exposed portions 655, 656, 657 and 658 of the blocking oxide layer 621 aare also depicted. In this configuration, the sacrificial material isremoved for the drain-side select gate layers and the drain-side dummymemory cells. The sacrificial material is not substantially removed forthe source-side select gate layers, source-side dummy memory cells anddata memory cells.

FIG. 6H1 depicts a semiconductor structure 659 which is an alternativeto the semiconductor structure of FIG. 6G, in an option in which thesacrificial material is also removed for the source-side select gatelayers and dummy memory cells, consistent with the semiconductorstructure of FIG. 6B. Voids 651 a, 652 a, 653 a and 654 a are formed inSGS1, SGS2, DWLL2 a and DWLL2 b, respectively. In this configuration,the sacrificial material is still not substantially removed for the datamemory cells. Exposed portions 651 b, 652 b, 653 b and 654 b of theblocking material 621 a are depicted.

FIG. 6H2 depicts a semiconductor structure 659 a obtained by processingthe semiconductor structure of FIG. 6H1 in accordance with step 508 ofFIG. 5. The etching process continues by removing portions of theblocking material, thereby exposing portions of the charge-trappingmaterial. Exposed portions 651 c, 652 c, 653 c and 654 c of thecharge-trapping material 622 a are depicted. A height of each portion ofthe blocking material which is removed is the same as the height of theassociated control gate layer. Portions of the blocking material whichare between the control gate layers, and coincident with the dielectriclayers, are not removed in this example.

FIG. 6I depicts a semiconductor structure 660 obtained by processing thesemiconductor structure of FIG. 6G in accordance with step 508 and 509of FIG. 5, where the tunneling material remains. The etching processcontinues by removing portions of the blocking material and thecharge-trapping material, thereby exposing portions of the tunnelingmaterial. Exposed portions 661, 662, 663 and 664 of the tunnelingmaterial 623 a are depicted. A height of each portion of the blockingmaterial and the charge-trapping material which is removed is the sameas the height of the associated control gate layer. Portions of theblocking material and the charge-trapping material which are between thecontrol gate layers, and coincident with the dielectric layers, are notremoved in this example.

FIG. 6J depicts a semiconductor structure 665 obtained by processing thesemiconductor structure of FIG. 6I in accordance with step 509 a of FIG.5, where the tunneling material is etched away and a dopant isintroduced laterally to the channel material. Exposed portions 666, 667,668 and 669 of the channel material 624 a are depicted. A dopant in drygas form, for instance, flows into the slits and voids to reach theexposed portions of the channel material. The flow is depicted by dashedlines 665 a and 665 b. For example, a p-type dopant can be used toincrease the Vth of the associated select gate transistors and dummymemory cells. As mentioned in connection with step 514 of FIG. 5, ann-type dopant can be used to decrease the Vth of the associated selectgate transistors and dummy memory cells. Typically, it is desirable toincrease the Vth rather than decrease it. The Vth of the select gatetransistors and dummy memory cells should be high enough (e.g., 2-3 V)so that these transistors are in a non-conductive state when 0 V isapplied to their control gates.

FIG. 6K depicts a semiconductor structure 670 obtained by processing thesemiconductor structure of FIG. 6I in accordance with step 511 of FIG.5. After the sacrificial material and the charge-trapping material hasbeen removed from the desired layers and any lateral doping has beenperformed in the channel material, the sacrificial material of theremaining control gate layers can be removed. The remaining control gatelayers include SGS1, SGS2, DWLL2 a, DWLL2 b and WLL0-WLL10, in thisexample. Voids are therefore formed in each of the control gates layers.For example, voids 671, 672, 673, 674, 675, 676, 677, 678, 679, 671 a,672 a, 673 a, 674 a, 675 a and 676 a are formed in WLL10, WLL9, WLL8,WLL7, WLL6, WLL5, WLL4, WLL3, WLL2, WLL1, WLL0, DWLL2 b, DWLL2 a, SGS2and SGS1, respectively. This is in addition to the voids 651, 652, 653and 654 which are formed in SGD1, SGD2, DWLL1 a and DWLL1 b,respectively.

FIG. 6L depicts a semiconductor structure 680 obtained by processing thesemiconductor structure of FIG. 6K in accordance with step 513 of FIG.5, where metal is deposited in the voids and slits. A metal 681 such astungsten tends to fill the voids and the slits. Before the metal isdeposited, other materials such as a high-k material and a metal barrierlayer can be deposited in the voids. In some cases, the width of theslit is greater than the height of the voids and the metal fills thevoids but coats the sidewalls of the slits without entirely filling theslits.

FIG. 6M depicts a semiconductor structure 682 obtained by processing thesemiconductor structure of FIG. 6L in accordance with step 513 of FIG.5, to remove the previously-deposited metal, provide an insulating layer683 in the slit, etch through the insulating layer at a bottom 683 a ofthe slit, and deposit additional metal 683 b to form metal-filled slits.The previously-deposited metal in the slits (shown in FIG. 6L) isremoved, e.g., by dry etching, to remove a conductive path between thecontrol gate layers which prevents independent driving of the controlgate layers. The opening at the bottom of the slit allows the metal inthe slit to contact the source line SL to provide a conductiveinterconnect to the top of the stack. Appropriate masks are used at thetop of the stack outside the slit when etching away thepreviously-deposited metal in the slit, and to deposit the insulatinglayer and the additional metal in the slit. CMP can be performed toremove excess amounts of the previously-deposited metal, insulatinglayer, additional metal and mask above the stack to arrive at thestructure in this figure. In another approach, an insulating materialentirely fills the slit after the previously-deposited metal in the slitis removed. In this case, the slit does not act as a verticalinterconnect.

FIG. 6N depicts a semiconductor structure 685 obtained by processing thesemiconductor structure of FIG. 6M in accordance with step 514 of FIG.5. Dopant can be applied to the top of the stack using ion implantationas depicted by arrows 686. A p-type dopant can be used to increase theVth of the associated select gate transistors and dummy memory cells andan n-type dopant can be used to decrease the Vth of the associatedselect gate transistors and dummy memory cells. The energy of the ionimplantation and an associated annealing (heating) time and temperaturecan be controlled so that the ions are implanted to a depth whichencompasses the channel material of the control gate layers of theselect gate transistors and/or dummy memory cells. In this example, thedoping occurs in a portion 687 of the channel material but not in aportion 689 of the channel material. That is, the doping can occur froma top of the stack down to a height h in the stack, in one approach.Optionally, the ion implantation can be controlled such that a dopingconcentration is different for the select gate transistors compared tothe dummy memory cells. The doping concentration could also be differentfor different select gate transistors and/or for different dummy memorycells. A mask 688 may be used to prevent ion implantation outside thememory hole area, and to limit the ion implantation to the memory hole.

FIG. 6O depicts a semiconductor structure 690 obtained by processing thesemiconductor structure of FIG. 6K in accordance with steps 512 and 513of FIG. 5. In step 512, in particular, a blocking oxide layer 691 can bedeposited in the voids of the control gate layers before the metal isdeposited. The blocking oxide layer can be provided in the voids when ablocking oxide layer is not provided along the sidewalls of the memoryholes. Or, the blocking oxide layer in the voids can be in addition to ablocking oxide layer along the sidewalls of the memory holes. Theblocking oxide layer in the voids of the control gate layers of theselect gate transistors and/or dummy memory cells ensures that theassociated control gate metal does not contact the channel material.

FIG. 7A depicts a semiconductor structure 700 obtained by processing thesemiconductor structure of FIG. 6C in accordance with step 503 of FIG.5. In this case, the blocking oxide layer is not provided in the memoryholes. A charge-trapping material 701 is deposited, followed by atunneling material 702 and a channel material 703.

FIG. 7B depicts a semiconductor structure 710 obtained by processing thesemiconductor structure of FIG. 7A in accordance with steps 504, 505 and507 of FIG. 5. After openings 705 and 706 are formed at the bottom ofthe memory holes to allow the channel material to communicate with thesource line, a core filler 704 is blanket deposited over the otherlayers of FIG. 7A. CMP is performed to planarize the top surface of thestack. The remaining portions of the materials along the sidewalls ofthe memory holes are depicted, including the charge-trapping material701 a, the tunneling material 702 a and the channel material 703 a.

Subsequently, the slits are formed, and the sacrificial material isselectively removed so that voids 711, 712, 713 and 714 are formed inSGD1, SGD2, DWLL1 a and DWLL1 b, respectively. Exposed portions 715,716, 717 and 718 of the charge-trapping material 701 a are alsodepicted.

FIG. 7C depicts a semiconductor structure 720 obtained by processing thesemiconductor structure of FIG. 7B in accordance with steps 509, 511,512 and 513 of FIG. 5. In step 512, in particular, a blocking oxidelayer 721 can be deposited in the voids of the control gate layersbefore the metal is deposited.

FIG. 8A depicts a semiconductor structure 800 obtained by processing asemiconductor structure in accordance with step 500 b of FIG. 5. In thiscase, all of the control gate layers comprise a common sacrificialmaterial, e.g., SiN. The initial fabrication of the stack is thereforesimplified compared to the case of using different sacrificialmaterials.

FIG. 8B depicts a semiconductor structure 810 obtained by processing thesemiconductor structure of FIG. 8A in accordance with step 506 a of FIG.5. After the slits 811 and 812 are etched, a protective layer 813 isdeposited in the slits and extends along sidewalls 814 of the slits.

FIG. 8C depicts a semiconductor structure 820 obtained by processing thesemiconductor structure of FIG. 8B in accordance with step 506 b of FIG.5. The protective layer is etched down to a specified height h in thestack which is, e.g., between a bottommost control gate layer (DWLL1 b)of the control gate layers for the dummy memory cells and/or the selectgate transistors and a topmost control gate layer (WLL10) of the controlgate layers for the data memory cells. That is, the specified height isdefined such that the charge-trapping material is removed from thecontrol gate layers which are above the height but not from the controlgate layers which are below the height. A remaining portion 813 a of theprotective layer shields the sacrificial material of the control gatelayers below the height h in the stack from an etchant in the slit, sothat the etchant is used to remove the sacrificial material of thecontrol gate layers above but not below the height h in the stack.

FIG. 8D depicts a semiconductor structure 830 obtained by processing thesemiconductor structure of FIG. 8C in accordance with steps 507, 508 and509 of FIG. 5. An etchant is provided via the slits to remove thesacrificial material of the control gate layers above the height h inthe stack. Additional etchants can remove portions of the blocking oxidelayer 831 and the charge-trapping layer 832 and thereby expose portionsof the tunneling material 833. The channel material 834 and core filler835 are also depicted. Voids 836, 837, 838 and 839 are formed in SGD1,SGD2, DWLL1 a and DWLL1 b, respectively. Exposed portions 840, 841, 842and 843 of the tunneling material 833 are also depicted.

Subsequently, steps 510, 511 and 513 can be performed to obtain thesemiconductor structure of FIG. 6M, or steps 510, 511, 512 and 513 canbe performed to obtain the semiconductor structure of FIG. 7C, forexample.

FIG. 9A depicts a semiconductor structure 900 obtained by processing thesemiconductor structure of FIG. 8A in accordance with step 505 of FIG.5. In this case, the etching of the slits can occurs in two steps. In afirst step, the slits are etched partway down the stack, to thespecified height h in the stack which is, e.g., between a bottommostcontrol gate layer of the control gate layers for the dummy memory cellsand/or the select gate transistors and a topmost control gate layer ofthe control gate layers for the data memory cells. Partial slits 901 and902 are formed. The control gate layers which are above but not belowthis height are then processed to remove the sacrificial material andthe charge-trapping material, such as depicted in FIG. 9B. In a secondstep, the slits are etched down to the bottom of the stack and fullslits are formed, such as the slit 641 or 642 in FIG. 6I. The controlgate layers which are below the height h are then processed to removethe sacrificial material. In this approach, a common sacrificialmaterial may be used for all of the control gate layers. In the memoryholes, the blocking oxide layer 903, charge-trapping layer 904,tunneling material 905, channel material 906 and core filler 907 arealso depicted.

FIG. 9B depicts a semiconductor structure 910 obtained by processing thesemiconductor structure of FIG. 9A in accordance with steps 507 and 509b of FIG. 5. An etchant is provided via the slits to remove thesacrificial material of the control gate layers above the height h inthe stack. Additional etchants can remove portions of the blocking oxidelayer 903 and the charge-trapping layer 904 and thereby expose portionsof the tunneling material 905. Specifically, exposed portions 915, 916,917 and 918 of the tunneling material 905 are also depicted. The channelmaterial 906 and core filler 907 are also depicted. Voids 911, 912, 913and 914 are formed in SGD1, SGD2, DWLL1 a and DWLL1 b, respectively.

While many of the above figures depict a straight NAND stringconfiguration, the techniques described herein can be applied to aU-shaped NAND string as well. As depicted in FIG. 2C, for example, asingle layer of the stack can includes both drain-side and source-sideselect gate transistors or dummy memory cells. As a result, theprocessing of the single layer can result in removal of thecharge-trapping material from the drain-side and source-side select gatetransistors or dummy memory cells.

Accordingly, it can be seen that, in one embodiment, a method forfabricating a memory device (100) comprises: a) forming a stack (231,376, 440) comprising alternating control gate layers (SGS1, SGS2, DWLL2a and DWLL2 b, WLL0-WLL10, DWLL1 b, DWLL1 a, SGD2 and SGD1) anddielectric layers (D0-D19), the control gate layers of the stackcomprise a control gate layer (SGS1, SGS2, DWLL2 a and DWLL2 b) for afirst transistor (490-493) above control gate layers (WLL0-WLL10) fordata memory cells (MC), the control gate layer for the first transistorcomprises a first sacrificial material (602, 603) and the control gatelayers for the data memory cells comprises a second sacrificial material(604); b) forming a memory hole (410, 411, 611, 612, MH0-MH3, MHx, MHy)in the stack, the memory hole having a sidewall (814, SW); c) depositinga charge-trapping material (622, 622 a, 701, 701 a, 832, 904), atunneling material (TM, 464) and a channel material (623, 623 a, 703,703 a, 834, 906) along the sidewall, wherein the charge-trappingmaterial is deposited before the tunneling material, and the tunnelingmaterial is deposited before the channel material; d) etching a slit(206, 239-243, 245, 247, 248, 346-348, 357-361, 641, 642, 811, 812) inthe stack; e) providing an etchant in the slit which is more selectiveof the first sacrificial material than the second sacrificial materialto etch away the first sacrificial material, creating a void (651-654,651 a-654 a, 711-714, 836-839, 911-914) in the control gate layer forthe first transistor and exposing a portion (651 c, 652 c, 653 c and 654c) of the charge-trapping material in the control gate layer for thefirst transistor; f) providing an etchant in the slit to etch away theportion of the charge-trapping material which is in the control gatelayer for the first transistor; g) providing an etchant in the slit toetch away the second sacrificial material, creating voids (671-679, 671a-676 a) in the control gate layers for the data memory cells; h)depositing a metal (681) in the slit, the metal fills the void in thecontrol gate layer for the first transistor and the voids in the controlgate layers for the data memory cells, wherein portions (MCb) of thecharge-trapping material in the control gate layers for the data memorycells remain in the memory device; and i) providing a blocking oxidelayer (471, 621, 621 a, 691, 721, 831, 903) between the charge-trappingmaterial and the metal.

In another embodiment, a method for fabricating a memory devicecomprises: a) forming a stack comprising alternating control gate layersand dielectric layers, the control gate layers of the stack comprise acontrol gate layer for a first transistor above control gate layers fordata memory cells; b) forming a memory hole in the stack, the memoryhole having a sidewall; c) depositing a charge-trapping material, atunneling material and a channel material along the sidewall, whereinthe charge-trapping material is deposited before the tunneling material,and the tunneling material is deposited before the channel material; d)etching a slit in the stack; e) depositing a protective layer in theslit; f) etching down the protective layer to a height in the stackwhich is between the control gate layer for the first transistor and thecontrol gate layers for the data memory cells, exposing a sacrificialmaterial of the control gate layer for the first transistor to the slitand leaving a remaining portion of the protective layer which shields asacrificial material of the control gate layers for the data memorycells from the slit; g) providing an etchant in the slit which etchesaway the sacrificial material of the control gate layer for the firsttransistor, creating a void in the control gate layer for the firsttransistor and exposing a portion of the charge-trapping material in thecontrol gate layer for the first transistor; h) providing an etchant inthe slit to etch away the portion of the charge-trapping material whichis in the control gate layer for the first transistor; i) providing anetchant in the slit which etches away the remaining portion of theprotective layer, exposing the sacrificial material of the control gatelayers for the data memory cells to the slit; j) providing an etchant inthe slit which etches away the sacrificial material of the control gatelayers for the data memory cells, creating voids in the control gatelayers for the data memory cells; k) depositing a metal in the slit, themetal fills the void in the control gate layer for the first transistorand the voids in the control gate layers for the data memory cells,wherein portions of the charge-trapping material in the control gatelayers for the data memory cells remain in the memory device; and 1)providing a blocking oxide layer between the charge-trapping materialand the metal.

In another embodiment, a method for fabricating a memory devicecomprises: a) forming a stack comprising alternating control gate layersand dielectric layers, the control gate layers of the stack comprise acontrol gate layer for a first transistor above control gate layers fordata memory cells; b) forming a memory hole in the stack, the memoryhole having a sidewall; c) depositing a charge-trapping material, atunneling material and a channel material along the sidewall, whereinthe charge-trapping material is deposited before the tunneling material,and the tunneling material is deposited before the channel material; d)etching a slit in the stack down from a top of the stack to a height inthe stack which is between the control gate layer for the firsttransistor and the control gate layers for the data memory cells; e)providing an etchant in the slit which etches away a sacrificialmaterial of the control gate layer for the first transistor, creating avoid in the control gate layer for the first transistor and exposing aportion of the charge-trapping material in the control gate layer forthe first transistor; f) providing an etchant in the slit to etch awaythe portion of the charge-trapping material which is in the control gatelayer for the first transistor; g) etching the slit down from the heightto a bottom of the stack, exposing the sacrificial material of thecontrol gate layers for the data memory cells to the slit; h) providingan etchant in the slit which etches away the sacrificial material of thecontrol gate layers for the data memory cells, creating voids in thecontrol gate layers for the data memory cells; i) depositing a metal inthe slit, the metal fills the void in the control gate layer for thefirst transistor and the voids in the control gate layers for the datamemory cells, wherein portions of the charge-trapping material in thecontrol gate layers for the data memory cells remain in the memorydevice; and j) providing a blocking oxide layer between thecharge-trapping material and the metal.

In another embodiment, a method for fabricating a memory devicecomprises: forming a stack comprising a plurality of layers, theplurality of layers comprise a first set of layers and a second set oflayers above the first set of layers, the first set of layers comprisesnitride layers alternating with oxide layers and the second set oflayers comprises polysilicon layers alternating with oxide layers;forming a memory hole in the stack, the memory hole having a sidewall;depositing charge-trapping layers and a channel material along thesidewall, wherein the charge-trapping layers are deposited before thechannel material; etching a void (e.g., slit) in the stack; providing anetchant in the void which is more selective of the polysilicon than theoxide or the nitride, creating voids in place of the polysilicon layersand exposing portions of the charge-trapping layers; providing anetchant in the void to etch away the portions of the charge-trappinglayers; providing an etchant which is more selective of the nitride thanthe oxide, creating voids in place of the nitride layers and exposingother portions of the charge-trapping layers; and depositing a metal inthe void, wherein the metal fills the voids in place of the polysiliconlayers and the voids in place of the nitride layers, wherein the otherportions of the charge-trapping layers remain in the memory device. Thesecond set of layers comprise one or more select gate transistors and/orone or more dummy memory cells.

The foregoing detailed description of the invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteachings. The described embodiments were chosen in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto.

What is claimed is:
 1. A method for fabricating a memory device,comprising: forming a stack comprising a first set of sacrificial layersabove a second set of sacrificial layers, wherein the first set ofsacrificial layers comprise a first sacrificial material and arearranged alternatingly with respective dielectric layers, the second setof sacrificial layers comprise a second sacrificial material and arearranged alternatingly with respective dielectric layers, and no twosacrificial layers comprising the first sacrificial material in thefirst set of sacrificial layers have a sacrificial layer comprising thesecond sacrificial material between them; forming a memory hole in thestack, the memory hole having a sidewall; depositing a charge-trappingmaterial, a tunneling material and a channel material along thesidewall, wherein the charge-trapping material is deposited before thetunneling material, and the tunneling material is deposited before thechannel material; etching a slit in the stack; providing an etchant inthe slit which is more selective of the first sacrificial material thanthe second sacrificial material to etch away the first sacrificialmaterial, creating a first set of voids and exposing a portion of thecharge-trapping material in each void of the first set of voids;providing an etchant in the slit to etch away the portion of thecharge-trapping material which is exposed in each void of the first setof voids; providing an etchant in the slit to etch away the secondsacrificial material, creating a second set of voids; depositing a metalin the slit, the metal fills the first set of voids and the second setof voids, wherein portions of the charge-trapping material adjacent tothe second set of voids remain in the memory device; and providing ablocking oxide layer between the charge-trapping material and the metal.2. The method of claim 1, wherein: the metal in the first set of voidscomprises a control gate for a select gate transistor.
 3. The method ofclaim 1, wherein: the metal in the first set of voids comprises acontrol gate for a dummy memory cell.
 4. The method of claim 1, whereinthe metal in the first set of voids comprises a control gate layer for afirst transistor, the method further comprising: performing ionimplantation at a top of the stack to provide a dopant in the channelmaterial, the dopant is provided at a portion of the channel materialwhich is adjacent to at least one of the voids of the first set ofvoids.
 5. The method of claim 1, further comprising: after the providingthe etchant in the slit to etch away the portion of the charge-trappingmaterial which is exposed in each void of the first set of voids,providing an etchant in the slit and in each void in the first set ofvoids etch away a portion of the tunneling material and expose a portionof the channel material; and via the slit, providing a dopant in eachvoid in the first set of voids to expose the portion of the channelmaterial to the dopant.
 6. The method of claim 1, wherein: the firstsacrificial material comprises polysilicon; the second sacrificialmaterial comprises nitride; and the dielectric layers comprise oxide. 7.The method of claim 1, wherein: the first sacrificial material comprisespolysilicon; the second sacrificial material comprises nitride; and theetchant in the slit which is more selective of the first sacrificialmaterial than the second sacrificial material comprises tetra methylammonium hydroxide.
 8. The method of claim 1, wherein: the etchant inthe slit to etch away the portion of the charge-trapping material whichis exposed in each void of the first set of voids comprises a chemicaldry etchant.
 9. The method of claim 1, wherein: the providing theblocking oxide layer comprises depositing the blocking oxide layer viathe slit, and the blocking oxide layer extends in each void of the firstset of voids and in each void of the second set of voids.
 10. The methodof claim 1, wherein the providing the blocking oxide layer comprisesdepositing the blocking oxide layer along the sidewall before thedepositing of the charge-trapping material, the method furthercomprising: before the providing the etchant in the slit to etch awaythe portion of the charge-trapping material in each void of the firstset of voids, providing an etchant in the slit and in each void of thefirst set of voids to etch away a portion of the blocking oxide layer ineach void of the first set of voids.
 11. The method of claim 10, furthercomprising: providing an etchant in the slit and in each void of thefirst set of voids to etch away a portion of the blocking oxide layerwhich is in each void of the set of voids, before the providing theetchant in the slit to etch away the portion of the charge-trappingmaterial which is in each void of the first set of voids.
 12. The methodof claim 1, wherein: the charge-trapping material comprises siliconnitride; the tunneling material comprises oxide; and the channelmaterial comprises polysilicon.
 13. The method of claim 1, wherein: themetal in the first set of voids comprises a control gate for a selectgate transistor; the metal in the second set of voids comprise controlgates for data memory cells; the data memory cells are seriallyconnected in a NAND string; the NAND string has a drain-side and asource-side; and the select gate transistor is at the drain-side. 14.The method of claim 1, further comprising: removing a portion of themetal which remains in the slit; providing an insulating layer in theslit; etching through the insulating layer at a bottom of the slit; anddepositing additional metal to form a metal-filled slit.
 15. The methodof claim 1, wherein: no two sacrificial layers comprising the secondsacrificial material have a sacrificial layer comprising the firstsacrificial material between them.
 16. The method of claim 1, wherein:the metal in the second set of voids comprise control gates for datamemory cells.
 17. A method for fabricating a memory device, comprising:forming a stack comprising a first set of sacrificial layers and asecond set of sacrificial layers, wherein the first set of sacrificiallayers comprise a first sacrificial material and are arrangedalternatingly with respective dielectric layers, the second set ofsacrificial layers comprise a second sacrificial material and arearranged alternatingly with respective dielectric layers, and no twosacrificial layers comprising the second sacrificial material in thesecond set of sacrificial layers have a sacrificial layer comprising thefirst sacrificial material between them; forming a memory hole in thestack, the memory hole having a sidewall; depositing a charge-trappingmaterial, a tunneling material and a channel material along thesidewall, wherein the charge-trapping material is deposited before thetunneling material, and the tunneling material is deposited before thechannel material; etching a slit in the stack; providing an etchant inthe slit which is more selective of the first sacrificial material thanthe second sacrificial material to etch away the first sacrificialmaterial, creating a first set of voids and exposing a portion of thecharge-trapping material in each void of the first set of voids;providing an etchant in the slit to etch away the portion of thecharge-trapping material which is exposed in each void of the first setof voids; providing an etchant in the slit to etch away the secondsacrificial material, creating a second set of voids; depositing a metalin the slit, the metal fills the first set of voids and the second setof voids, wherein portions of the charge-trapping material adjacent tothe second set of voids remain in the memory device; and providing ablocking oxide layer between the charge-trapping material and the metal.18. The method of claim 17, wherein: the first set of sacrificial layersare arranged above a specified height in the stack; and the second setof sacrificial layers are arranged below the specified height in thestack.
 19. The method of claim 17, wherein: no two sacrificial layerscomprising the first sacrificial material have a sacrificial layercomprising the second sacrificial material between them.
 20. The methodof claim 17, wherein: the metal in the second set of voids comprisecontrol gates for data memory cells.
 21. The method of claim 17,wherein: the metal in the first set of voids comprises a control gatefor a select gate transistor.
 22. The method of claim 17, wherein: themetal in the first set of voids comprises a control gate for a dummymemory cell.